Calling destroy_hist_field() on an expression will recursively free
any operands associated with the expression. If during expression
parsing the operands of the expression are already set when an error
is encountered, there is no need to explicity free the operands. Doing
so will result in destroy_hist_field() being called twice for the
operands and lead to a use-after-free (UAF) error.
Fix this by only calling destroy_hist_field() for the expression if the
operands are already set.
Signed-off-by: Kalesh Singh <[email protected]>
Fixes: 8b5d46fd7a38 ("tracing/histogram: Optimize division by constants")
Reported-by: kernel test robot <[email protected]>
---
kernel/trace/trace_events_hist.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 5ea2c9ec54a6..e3856eaf2ac3 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -2669,7 +2669,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
if (!divisor) {
hist_err(file->tr, HIST_ERR_DIVISION_BY_ZERO, errpos(str));
ret = -EDOM;
- goto free;
+ goto free_expr;
}
/*
@@ -2709,7 +2709,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
expr->type = kstrdup_const(operand1->type, GFP_KERNEL);
if (!expr->type) {
ret = -ENOMEM;
- goto free;
+ goto free_expr;
}
expr->name = expr_str(expr, 0);
@@ -2719,6 +2719,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
free:
destroy_hist_field(operand1, 0);
destroy_hist_field(operand2, 0);
+free_expr:
destroy_hist_field(expr, 0);
return ERR_PTR(ret);
base-commit: 8ab774587903771821b59471cc723bba6d893942
--
2.34.0.rc1.387.gb447b232ab-goog
On Tue, 16 Nov 2021 18:12:22 -0800
Kalesh Singh <[email protected]> wrote:
> Calling destroy_hist_field() on an expression will recursively free
> any operands associated with the expression. If during expression
> parsing the operands of the expression are already set when an error
> is encountered, there is no need to explicity free the operands. Doing
> so will result in destroy_hist_field() being called twice for the
> operands and lead to a use-after-free (UAF) error.
>
> Fix this by only calling destroy_hist_field() for the expression if the
> operands are already set.
>
> Signed-off-by: Kalesh Singh <[email protected]>
> Fixes: 8b5d46fd7a38 ("tracing/histogram: Optimize division by constants")
> Reported-by: kernel test robot <[email protected]>
> ---
> kernel/trace/trace_events_hist.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 5ea2c9ec54a6..e3856eaf2ac3 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -2669,7 +2669,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
> if (!divisor) {
> hist_err(file->tr, HIST_ERR_DIVISION_BY_ZERO, errpos(str));
> ret = -EDOM;
> - goto free;
> + goto free_expr;
> }
>
> /*
> @@ -2709,7 +2709,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
> expr->type = kstrdup_const(operand1->type, GFP_KERNEL);
> if (!expr->type) {
> ret = -ENOMEM;
> - goto free;
> + goto free_expr;
> }
>
> expr->name = expr_str(expr, 0);
> @@ -2719,6 +2719,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
> free:
> destroy_hist_field(operand1, 0);
> destroy_hist_field(operand2, 0);
> +free_expr:
> destroy_hist_field(expr, 0);
>
> return ERR_PTR(ret);
>
> base-commit: 8ab774587903771821b59471cc723bba6d893942
Wouldn't this be a simpler and more robust fix?
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 5ea2c9ec54a6..aab69b4ffe11 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -2717,8 +2717,10 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
return expr;
free:
- destroy_hist_field(operand1, 0);
- destroy_hist_field(operand2, 0);
+ if (!expr || expr->operand[0] != operand1)
+ destroy_hist_field(operand1, 0);
+ if (!expr || expr->operand[1] != operand2)
+ destroy_hist_field(operand2, 0);
destroy_hist_field(expr, 0);
return ERR_PTR(ret);
I'm worried about the complexity of having to know where to free what,
and not just figuring it out at the end.
-- Steve
On Tue, Nov 16, 2021 at 7:47 PM Steven Rostedt <[email protected]> wrote:
>
> On Tue, 16 Nov 2021 18:12:22 -0800
> Kalesh Singh <[email protected]> wrote:
>
> > Calling destroy_hist_field() on an expression will recursively free
> > any operands associated with the expression. If during expression
> > parsing the operands of the expression are already set when an error
> > is encountered, there is no need to explicity free the operands. Doing
> > so will result in destroy_hist_field() being called twice for the
> > operands and lead to a use-after-free (UAF) error.
> >
> > Fix this by only calling destroy_hist_field() for the expression if the
> > operands are already set.
> >
> > Signed-off-by: Kalesh Singh <[email protected]>
> > Fixes: 8b5d46fd7a38 ("tracing/histogram: Optimize division by constants")
> > Reported-by: kernel test robot <[email protected]>
> > ---
> > kernel/trace/trace_events_hist.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> > index 5ea2c9ec54a6..e3856eaf2ac3 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -2669,7 +2669,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
> > if (!divisor) {
> > hist_err(file->tr, HIST_ERR_DIVISION_BY_ZERO, errpos(str));
> > ret = -EDOM;
> > - goto free;
> > + goto free_expr;
> > }
> >
> > /*
> > @@ -2709,7 +2709,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
> > expr->type = kstrdup_const(operand1->type, GFP_KERNEL);
> > if (!expr->type) {
> > ret = -ENOMEM;
> > - goto free;
> > + goto free_expr;
> > }
> >
> > expr->name = expr_str(expr, 0);
> > @@ -2719,6 +2719,7 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
> > free:
> > destroy_hist_field(operand1, 0);
> > destroy_hist_field(operand2, 0);
> > +free_expr:
> > destroy_hist_field(expr, 0);
> >
> > return ERR_PTR(ret);
> >
> > base-commit: 8ab774587903771821b59471cc723bba6d893942
>
> Wouldn't this be a simpler and more robust fix?
>
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 5ea2c9ec54a6..aab69b4ffe11 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -2717,8 +2717,10 @@ static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
>
> return expr;
> free:
> - destroy_hist_field(operand1, 0);
> - destroy_hist_field(operand2, 0);
> + if (!expr || expr->operand[0] != operand1)
> + destroy_hist_field(operand1, 0);
> + if (!expr || expr->operand[1] != operand2)
> + destroy_hist_field(operand2, 0);
> destroy_hist_field(expr, 0);
Hi Steve,
Agreed. What you suggested is simpler to work with. I'll respin a new version.
Thanks,
Kalesh
>
> return ERR_PTR(ret);
>
>
> I'm worried about the complexity of having to know where to free what,
> and not just figuring it out at the end.
>
> -- Steve